Magnetic time delay switch

ABSTRACT

A magnetic reed switch comprises an insulative housing in which are laterally spaced magnetic reeds. A coil of magnetic wire is wound around the housing. An adjustable clamp encircles the coil. The reeds, coil and clamp can be connected in a circuit to perform a time delay switching function which is variable over a wide range by adjustably positioning the clamp.

United States Patent Patented 361m 11. Wiegnnd as: Bllfillll' $1.,Valley Stream, N.Y. 11580 25,195

Apr. 2, 1970 Aug. 31, 1971 Inventor Appl. No. Filed MAGNETIC TIME DELAYSWITCH 10 Claims, 4 Drawing Fig.

us. c1. 335/146,

317/133, 335/154, 336/179 161.01 11011161/04 Field ofSearch 317/133;

[ References Cited UNITED STATES PATENTS 3,003,019 11/1961 Scheidig335/208 3,174,008 3/1965 Mishelevich et al. 335/154 3,284,735 11/1966Siiberg 335/208 X Primary Examiner-Bernard A-. Gilheany AssistantExaminer-R. N. Envall, Jr. AttorneyPolachek & Saulsbury ABSTRA CT: Amagnetic reed switch comprises an insulative housing in which arelaterally spaced magnetic reeds. A coil of magnetic wire is wound aroundthe housing. An adjustable clamp encircles the coil. The reeds, coil andclamp can be connected in a circuit to perform a time delay switchingfunction which is variable over a wide range by adjustably positioningthe clamp.

MAGNETIC TIMEDELAY swrrcn I This invention relates to the artof timedelay circuit devices and more particularly concerns a magnetictimedelay switch which is variable in time delay over a wide range.

- The most common devices currently used for performing time delayswitching functions employ either a thermally activated bimetallic strip.or a solid-state circuit. The electronic time delay devices areemployed where specifications are quite stringent as in military andspace flight equipment. Forgeneral industrial or commercial applicationsbimetallic ele- I the two contacts finally separate, thereby breakingthe circuit.

-' For a number of reasons it is desirable to replace this kind ofdevice with a radically differentconfiguration. The typical delay unitis a rather inefficient device. Normally the fullpower source voltage isplaced across the heatingelement, in parallel to the load. Enough energymust be pumped into the bimetallic element to very significantly raiseits temperature. Furthermore, the action of opening (or closing) a setof contacts is by its very nature slow, giving the problem of possiblearcing and brief periods of indeterminate switch positions.

' Mechanical means can be employed to cause the contacts to snap, andthis further adds to the complexity. The assembly of this thermostaticdelay requires precision, to insure that proper shape and positioning ofthe two metals to be joined are accurate. This does not lend itself veryeasily to a range of adjustments. It also does not lend itself tominiaturized packaging. Of ten the whole device is enclosed in a casewith a plug-in base, such as a tube. This is too bulky for manyapplications, and also may require that extra wiring be run from apushbutton or switch which is'located at a distant point more ing ordirect current operation and can work off power lines of readilyavailable voltages such as 12, 24 or 117 volts AC or DC. Productioncosts are significantly less than those of other types of time delayswitches. The use of bimetallic strips is avoided. Also eliminated aremechanical means for snapping contacts apart or together, resistors,capacitors, rectifiers,

transistors or any other solid-state or electronic tube components.Furthermore efficiency is improved over that attainable by use ofthermally responsive bimetallic strips or electronic circuit-type timedelay units. A further very important advantage is that the amount'oftime delay is adjustable over a wider range than is possible withcomparable conventional time delay units. I

Other and further features, objects and advantages will become apparentfrom the following detailed description taken together with the drawing,wherein:

FIG'. I is an oblique side view of a time delay switch embodying theinvention.

F IG. 2 is an enlarged cross-sectional view.

FIG. 3 is a longitudinal sectional view taken on line 3-3 of FIG. 2;

, FIG. 4 is a diagram of an electrical circuit embodying the invent-ion.

7 Referring first to FIGS. 1 2 and 3, the switch 10 comprises a tubularclosed housing 11 made of electrically insulative material such as glassor a suitable plastic. The housing is axially elongated andhas a thincylindrical wall 12 closed at opposite ends 14, 16. Two reeds 18 and 20made of magnetic material are longitudinally secured in the housing atends l4, 16. Free inner ends 19, 21 of the reeds are laterally spacedfrom each other but overlap slightly axially of the housing. Outer ends22, 24 of the reeds extend beyond the closed, sealed ends of thehousing. The reeds are flexible but sufficiently'and massive so thatthey do not make contact with each other for normal conditions ofvibration and shock. When a magnetic force of sufficient intensity isapplied the reeds can be brought together at their overlapped free ends.Removal of the magnetic influence will allow the reeds to spring-apartand assume their normal spaced position shown in FIGS. 2 and 3. In apractical application the reeds may be about 2 inches in overall lengthand the housing 11 may also be about 2 inches.

A magnetic wire made of iron-nickel or other suitable alloy is wound ina single layer-to form a coil25 around the housing 11 extending from oneend to the other of the cylindrical wall 12. One end 26 of the coil issecured by solder 28 to end portion 22 of reed 18. The other end 29 ofthe coil is left free. An electrically conductive cylindrical clamp 30encircles the coil and housing. Radially extending tabs 32 are abuttedand secured together by a screw 33. The clamp'30 can be moved axially ofthe coiland housing by loosening the screw. Tightening the screw locksthe clamp in place on the coil and housing. The location of the clampaxially long the coil determinesthe time delay action of the switch. Endportions 22 and 24 of the reeds andclarnp 30 may be further connected bywires 32, 34, 36 to external circuitry such as shown diagrammaticallyinFIG. 4. Screw 33 will hold wire 36 while solder joints 38, 39 willhold wires 32, 34.

FIG. 4 shows a manually operated'and activated time delay circuit 50. Apushbutton switch 52 which is normally open, is

' connected to the end portions of the reeds via wires 32 and 34 andbridges the reeds electrically when the pushbutton is pressed. When thepushbutton switch is closed, the external connected to end portion 24 ofreed 20. The circuit 16 is connected by wires 36 and 56 in series" withan external load device 60 which maybe a lamp, resistor, or the like,and terminals 62, 63 of a suitable electrical power source 64. The loadand be any device to which it is desired to apply power for apredetermined length of time after operating the, pushbutton switch 52.The impedance of the magnetic coil 25 will be small with respect to thatof the load device 60.

In operation of the circuitry of FIG. 4, when the pushbutton switch 52is closed by pressing the pushbutton, current flows from the powersource 64 via terminals 62, 63 through load device 60, wire 36, clamp30, through a portion of coil 25 located between clamp 30 and reed endportion 22, through wire 32, pushbutton switch 52, wire 34, reed endportion 24 and wire 56. The voltage developed across the magnetic coil25 between the clamp 30 and wire 32 small with respect to the voltageacross the load 60 or that of power source 64. The electrical currentflowing through coil 25 causes a magnetomotive force field to bedeveloped along the main axis of the coil and housing. The magneticreeds in the housing channelize the magnetic flux because of their lowpermeability, except for at the small discontinuity at the airgap Gbetween the reeds. The same current also creates miniature flux pathswithin the .wire coil itself. The magnetomotive force field between twofree ends of the reeds develops a mechanical force which tends to pullthem together as indicated by arrows, A, B. As soon as the reed end 19,21 contact each other they effectively short circuit the pushbuttonswitch 52 which may now be manually released to return to its normallyopen position. The current passing through the reeds I8, 20, in turn,

applies a magnetomotive force to the wire coil 25. Power will now bemaintained in the load via the contacting inner end portions of thereeds.

The external circuit will not remain closed indefinitely. The timeduration the external circuit will remain closed and power will besupplied to load device 60 will depend on the time delay characteristicof the switch 10. This time delay characteristic depends primarily onthe diameter of the wire coil 25, the position of the clamp 30 along thecoil, and the impedance of the load device. The characteristic dependsonly secondarily on the ambient temperature of the switch 10. Despitethe small percentage amount of power dissipated in the turns of coil 25it is enough to slowly raise the temperature of the coil. This increasein temperature has its effect on a molecular level. Much of thealignment of the magnetic domains in the wire of the coil 25 isdestroyed during the heating. The magnetomotive force along the mainaxis of the housing 11 decreases significantly. This force hadoriginally been just sufficient to close the contacts between the innerends of the reeds. Now, however, there is hysteresis to overcome. Sincethe reeds are touching, significantly less flux density still providesmore than adequate force to keep the inner reed ends 19,21, pressedtogether and allows the current to flow between the outer reed ends 22,24, since the necessary force is inversely proportional to theseparation between the reeds. However, as long as the current is soflowing the temperature continues to rise. The change in the netmagnetomotive force field will not be linear, but rather the complexinteractions of the fields will cause a self-eliminating feedback typeof interaction. Soon a point will be reached where the diminished fluxdensity no longer induces a force sufficient to overcome the entiretension no longer induces a force sufficient to overcome the entiretension in the reeds 18, 20. As the inner ends 19, 21, of the reedsbegin to separate, the electrical resistance through the reeds betweenends 22, 24, increases rapidly causing through collapse of the magneticfields thereby further reducing the holding force the reed ends 19, 21,at an extremely rapid rate. The force inherent in the tension of thereeds causes the ends 19, 21, of the reeds to snap apart. The circuit isbroken and current flow stops. The switch starts to cool rapidly. Thetime delay cycle has been completed. The length of this cycle is thetime interval between opening pushbutton switch 52 and opening ofcontact between reed ends 19, 2]. Throughout the entire cycle ofoperation the temperature never rises above 100 F. or so, so that theswitch is never too hot to touch at any point. The arrangement of thecircuitincluding switch 10 and pushbutton switch 52 will be very compactto occupy very small volume.

The above description of operation applies particularly to directcurrent operation. When alternating current is supplied by power source64, a permanent magnet 70 will be provided. This magnet will be movablydisposed adjacent the switch coil 25 to provide the magnetomotive forcereferred to above. The magnet may be coupled to the pushbutton switch soas to be moved into effective magnetomotive force inducing position onlywhen the pushbutton switch is closed. When the pushbutton is opened themagnet will be withdrawn beyond its effective magnetomotive forceinducing position. Otherwise operation of the circuitry will be same asdescribed above. The voltage developed across the portion of coil 25between clamp 30 and reed end 22 will be primarily due to the resistanceof the wire of coil'25 rather than its inductive reactance when ACcurrent is employed.

To summarize, the invention has the following desirable features:

l. The magnetic switch assembly performs a switching function withpredetermined time delay.

2. The time delay characteristic can be adjusted in time duration over awide range.

3. The time delay switch assembly can be constructed from a few simpleinexpensive components.

4. The basic components of the time delay switch assembly comprise aninsulative housing, a pair of magnetic reeds, a coil of magnetic wire,and cylindrical clamp.

5. The components of the assembly require only a very simple assemblyprocedure.

6. The time delay switch assembly may include a small pushbutton switchin a time delay switching circuit.

7. The time delay switching circuit will be compact and occupy a verysmall space. i y

8. The time delay switching circuit need have only two externalterminals.

9. The small size, small number of terminals and simplicity ofconstruction enable the circuit to be used in many applicationsheretofore unable to use conventional time delay devices.

10. The time delay switching circuit will maintain power to a loaddevice when series connected to the load and a power source, once thecircuit is activated, for a predetermined duration of time.

1 l. The device consumes so very little power that the load deviceconsumes substantially all the power supplied by the power source.

12. The time delay switching circuit has the inherent characteristic ofremoving power from the load instantaneously so that there is noindeterminate state between power-on and power-off.

13. The temperature of the time delay switch assembly never becomes toohot to handle manually.

14. The time delay switch assembly can operate in any desiredorientation or physical position.

15. The time delay switch assembly can be made to operate with an AC orDC power source.

16. The time delay switch assembly will operate with a wide range ofapplied line voltages.

17. The time delay adjustment is very easily and simply made by slidablyadjusting the clamp along the magnetic switch.

18. The time delay switching circuit can operate with predetermined timedelay for different loads by adjusting the position of the clamp alongthe magnetic switch.

19. The assembly tolerances of the reeds need not be as critical asthose of comparable bimetallic elements employed in time delay devices.

20. The time delay switch assembly will be highly reliable and certainin operation.

What is claimed is:

l. A time delay switching device, comprising a cylindrical insulativesupport; a helical coil of magnetic wire wound on said support; saidcoil wire composed of material which loses its magnetic permeabilityupon heating a pair of flexible magnetic reeds secured to opposite endsof said support and extending longitudinally inside said support, saidreeds having inner overlapping laterally spaced free inner ends, saidreeds having outer ends extending outwardly of opposite ends of saidcylindrical support, the outer end of one reed being connected to oneend of said coil, the other end of said coil being free; and aconductive member mounted on said support and slidable along said coilin contact therewith, and means for connecting said conductive memberand the outer end of the other one of said reeds is series with a sourceof electrical voltage and a resistive load, whereby momentary electricalconnection of the outer ends of said reeds will pass electrical currentthrough a part of said coil to generate a magnetomotive force, whichcauses said inner ends of the reeds to contact each other, and wherebyopening said electrical connection will leave said inner ends of thereeds contacting each other for a certain time duration while power issupplied to said load, whereupon said magnetomotive force will decreasedue to current through said coil, which causes heating thereof, untilthe contacting inner ends of the reeds separate and cut off the powersupplied to said load.

2. A time delay switching device as defined in claim 1, furthercomprising a switch having normally open contacts respectively connectedto the outer ends of the reeds, whereby closure of said switch to closesaid contacts establishes said electrical connection between the outerends of the reeds.

3.-A time delay switching device as defined in claim 2, wherein saidswitch is a manually operable pushbutton switch.

4. A time delay switching device as defined in claim 1, wherein saidconductive member has the form of a cylindrical clamp encircling saidsupport and coil in Contact with the coil, whereby said certain timeduration is determined by the position of said clamp axially along thecoil. I

5. A time delay switching device as defined in claim 4 furthercomprising a switch having normally open contacts respectively'connectedto the outer ends of the reeds, whereby closure of said switch to closesaid contacts establishes said electrical connection between the outerends of the reeds.

6. A time delay switching device as defined in claim 1, furthercomprising an electrical voltage source and a resistive load connectedin series circuit with each other, said circuit having two terminalsrespectively connected to said conductive member and said outer end ofthe other one of the reeds, said coil having an impedance which issmaller that that of said load so that substantially all of the powergenerated by said voltage source is consumed in said load.

7. A time delay switching device as defined in claim 6, wherein saidvoltage source supplies alternating current to the load and coil, saiddevice further comprising a permanent magnet movable disposed adjacentsaid coil for generating a magnetomotive force field between the spacedinner ends of the reeds when the magnet is momentarily disposedsufficiently close to the coil to cause said inner ends of the reeds tocontact eachother.

8. A time delay switching device as defined in claim 5, furthercomprising an electrical voltage source and a resistive load connectedin series circuit with each other, said circuit having two terminalsrespectively connected to said clamp and the outer end of said other oneof the reeds, said coil having an impedance which is smaller than thatof said load so that substantially all of the power generated bysaidvoltage source is consumed in said load.

9. A time delay switching device as defined in claim 8,

wherein said switch is a manually operable pushbutton switch. 1

10. A time delay switching device as defined in claim 9, wherein saidvoltage source supplies alternating current to the load and coil, saiddevice further comprising a permanent magnet movable disposed adjacentsaid coil for generating a magnetomotive force field between the spacedinner ends of the reeds when the magnet is momentarily disposedsufficiently close to the coil to cause said inner ends of the reeds tocontact each other.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3 602851 Dated August 31 197].

Inventor(s) John R. Wiegand It is certified that error appears in theabove-identified patent and that said Letters Patent are herebycorrected as shown below:

Column 2, line 44 after "terminals" insert "at wire 36 and" Column 2,line 50 and be" should read can be" Column 3, lines 31 34 after "entiretension" delete "no longer induces a force sufficient to overcome theentire tension" appearing after "entire tension" Column 3, line 36"through" should read "instant" Column 3, line 38 insert between afterholding force" Column 3, line 58 insert switch after "pushbutton" Column5, Claim 7, line 22 "moveable" should read "moveably" Column 6, Claim10, line 17 "moveable" should read "moveably" Signed and sealed this17th day of October 1972.

(SEAL) Attest:

EDWARD M.FLETCHJ:;R,JR. ROBERT GOTTSCI-LALK Attestlng OfficerCommissioner of Patents

1. A time delay switching device, comprising a cylindrical insulativesupport; a helical coil of magnetic wire wound on said support; saidcoil wire composed of material which loses its magnetic permeabilityupon heating a pair of flexible magnetic reeds secured to opposite endsof said support and extending longitudinally inside said support, saidreeds having inner overlapping laterally spaced free inner ends, saidreeds having outer ends extending outwardly of opposite ends of saidcylindrical support, the outer end of one reed being connected to oneend of said coil, the other end of said coil being free; and aconductive member mounted on said support and slidable along said coilin contact therewith, and means for connecting said conductive memberand the outer end of the other one of said reeds is series with a sourceof electrical voltage and a resistive load, whereby momentary electricalconnection of the outer ends of said reeds will pass electrical currentthrough a part of said coil to generate a magnetomotive force, whichcauses said inner ends of the reeds to contact each other, and wherebyopening said electrical connection will leave said inner ends of thereeds contacting each other for a certain time duration while power issupplied to said load, whereupon said magnetomotive force will decreasedue to current through said coil, which causes heating thereof, untilthe contacting inner ends of the reeds separate and cut off the powersupplied to said load.
 2. A time delay switching device as defined inclaim 1, further comprising a switch having normally open contactsrespectively connected to the outer ends of the reeds, whereby closureof said switch to close said contacts establishes said electricalconnection between the outer ends of the reeds.
 3. A time delayswitching device as defined in claim 2, wherein said switch is amanually operable pushbutton switch.
 4. A time delay switching device asdefined in claim 1, wherein said conductive member has the form of acylindrical clamp encircling said support and coil in contact with thecoil, whereby said certain time duration is determined by the positionof said clamp axially along the coil.
 5. A time delay switching deviceas defined in claim 4 further comprising a switch having normally opencontacts respectively connected to the outer ends of the reeds, wherebyclosure of said switch to close said contacts establishes saidelectrical connection between the outer ends of the reeds.
 6. A timedelay switching device as defined in claim 1, further comprising anelectrical voltage source and a resistive load connected in seriescircuit with each other, said circuit having two terminals respectivelyconnected to said conductive member and said outer end of the other oneof the reeds, said coil having an impedance which is smaller that thatof said load so that substantially all of the power generated by saidvoltage source is consumed in said load.
 7. A time delay switchingdevice as defined in claim 6, wherein said voltage source suppliesalternating current to the load and coil, said device further comprisinga permanent magnet movable disposed adjacent said coil for generating amagnetomotive force field between the spaced inner ends of the reedswhen the magnet is momentarily disposed sufficiently close to the coilto cause said inner ends of the reeds to contact each other.
 8. A timedelay switching device as defined in claim 5, further comprising anelectrical voltage source and a resistive load connected in seriescircuit with each other, said circuit having two terminals respectivelyconnected to said clamp and the outer end of said other one of thereeds, said coil having an impedance which is smaller than that of saidload so that substantially all of the power generated by said voltagesource is consumed in said load.
 9. A time delay switching device asdefined in claim 8, wherein said switch is a manually operablepushbutton switch.
 10. A time delay switching device as defined in claim9, wherein said voltage source supplies alternating current to the loadand coil, said device further comprising a permanent magnet movabledisposed adjacent said coil for generating a magnetomotive force fieldbetween the spaced inner ends of the reeds when the magnet ismomentarily disposed sufficiently close to the coil to cause said innerends of the reeds to contact each other.